The present invention relates to packet based cellular communication systems, and more particularly to methods and apparatuses for reducing reception and transmission times of communication equipment, thereby reducing power consumption in the communication equipment.
Cellular communications systems are becoming more and more packet oriented (e.g., utilizing the Internet Protocol—“IP”). For example, the Third Generation Partnership Project (3GPP) has extended Wideband Code Division Multiple Access (WCDMA) with High-Speed Packet Access (HSPA) which provides transport and control channels that are optimized with respect to packet services. It is expected that, in future systems, even typical circuit-switched services like speech will be transmitted by means of a packet based system (e.g., Voice over IP—“VoIP”). This is evidenced by, for example, the evolution of the HSPA standard, Continuous Packet Connectivity (CPC) (Release 7 of the 3GPP standard) being optimized for low data rate packet services like VoIP. As another example, the new Orthogonal Frequency Division Multiplex (OFDM) based system, Long-Term Evolution (LTE), will be a packet only based system, in which speech must be transmitted over VoIP.
Having a packet based structure makes it possible for a communications terminal to enter a “sleep” mode in between the reception and transmission of packets. Sleep modes typically involve disabling the radio transmitter and/or the radio receiver (in discontinuous transmission/discontinuous reception—“DTX/DRX”) as well as one or more other baseband processors used for modulation and demodulation of the radio signal. The use of DTX/DRX allows power consumption to be significantly reduced.
In packet based systems, packets are transmitted in the downlink (DL) direction as well as in the uplink (UL) direction. In either case, the transmission is considered to take place on what is throughout this document referred to as an “initiating link.” In modern packet-based systems, the recipient of a packet typically transmits information in the reverse direction (in what is throughout this document referred to as a “response link”) indicating whether a packet was correctly (Acknowledge, or “ACK”) or erroneously (Negative Acknowledge, or “NAK”) decoded (ACK/NAK signaling). If a NAK occurs, the packet is retransmitted. Hence, in the DL direction the base station transceiver (e.g., the “node B” in a Universal Mobile Telecommunications System—“UMTS”) transmits a data packet to the User Equipment (UE), the UE decodes the packet and transmits either an ACK or NAK up to the base station transceiver. If a NAK is transmitted, the same packet is retransmitted and the UE decodes that packet (either alone, in so-called “automatic repeat request”—“ARQ”—systems, or in combination with the earlier-received packet in so-called “hybrid automatic repeat request”—“HARQ”—systems). The same procedure takes place in the UL direction, however with the UE as transmitter and the base station transceiver as the receiver.
The protocol and timing of packet transmissions as well as the exact timing relationship between the transmission of packets and their corresponding ACK/NAKs are dependent on which specifications are in force. For example, in HSPA DL, the ACK/NAK should be transmitted from the UE approximately 5 ms after the reception of the DL packet, whereas the ACK/NAK for UL packets should be transmitted between 6.5-8.5 ms after receipt of the UL packet. As another example, in some systems (e.g., HSPA UL) the UE may transmit (small) packets without permission from the base station, whereas in other systems (e.g., LTE) the UE is always required to make a scheduling request, which asks for an allocation of UL resources for transmitting information.
In typical systems, utilization of the DL is separate from utilization of the UL; that is, DL packets are received independently of UL packets. This reduces the possibility of entering the DRX/DTX mode (and hence reduces the possibility of saving power) due to the need to turn the radio on both for transmitting/receiving packets and ACK/NAK control signaling.
Another important aspect of cellular systems is mobility. In order to be able to perform a handover, the UE must regularly take measurements of its environment. In HSPA as well as in LTE, reuse 1 is allowed, meaning that the neighbor cells transmit on the same carrier. Consequently, the present inventors have recognized that it is theoretically possible for the UE to simultaneously receive data and make DL signal strength measurements (intra-frequency measurements). However, in conventional systems, measurements for handover are made independently of packet reception and transmission which, because it further reduces the possibility of entering sleep mode, reduces the potential power savings that could otherwise be obtained by optimal use of DRX/DTX capability.
In view of the entire discussion above, it is evident that there is a need for methods and apparatuses that more optimally utilize the system potential to reduce power consumption.